Linda Poon is a staff writer at CityLab covering science and urban technology, including smart cities and climate change. She previously covered global health and development for NPR’s Goats and Soda blog.
The historic South Carolina city escaped the worst of the latest storm, but rising seas and an aging drainage system may soon bring chronic inundation.
When Hurricane Dorian grazed the coast of South Carolina on Wednesday and Thursday, the hurricane packed winds of more than 100 miles per hour, triggering massive power outages throughout the state. Mayor John Tecklenburg of Charleston issued a mandatory evacuation order for that city ahead of the storm, warning of a “triple threat”: heavy rain, a deadly storm surge, and an above-average high tide.
Though the storm pummeled Charleston with heavy rainfall and threatened a 10-foot storm surge along Charleston Harbor, the city escaped that worst-case scenario—Dorian weakened to a Category 2 while traveling up the East Coast. Streets in low-lying parts of Charleston flooded. But these days, it doesn’t take a hurricane to do that.
Days before Dorian’s arrival, a naturally occurring “king tide” unrelated to the hurricane reached more than 8 feet, surpassing Charleston’s high-tide average of 5.5 feet. Streets typically begin flooding when tides reach 7 feet high, and this is becoming a chronic threat to the city. So while Dorian threatened historic flooding to Charleston, the reality is that it no longer takes extreme weather to inundate the city.
The city’s director of sustainability, Katie McKain, told NPR that flooding is often forecasted once a week, and that her department is planning for a two-to-three-feet rise in sea level over the next 50 years. (Neither McKain nor Charleston’s chief resilience officer could be reached by CityLab in time for publication.) As the National Oceanic and Atmospheric Administration wrote in its recent report on high-tide flooding, Charleston already saw roughly five flood days between May 2018 and April 2019 (though that doesn’t capture every instance of flooding). Over that same period, the harbor’s tidal gauges exceeded 7 feet on 44 days.
Such “nuisance” or “sunny day” flooding is becoming more common as climate change accelerates sea level rise and extreme rain events. Nationally, cities can expect a median of 7 to 15 days of high-tide flooding each year by 2030, and 25 to 75 days by 2050, according to the NOAA report.
That prediction spells big trouble for many coastal cities, but especially ones like Charleston, whose stock of 18th-century homes and buildings are located in a vulnerable low-lying downtown. “These cities have an amazing cultural legacy that is important in two respects: We want to both preserve it and have it continue to be a tourism draw,” says Kristina Dahl, a senior climate scientist focusing on sea level rise at the Union of Concerned Scientists. “These historic districts are important engines for the local economy.” In 2018, the greater Charleston area raked in 7.3 million visitors and record $8 billion in tourism-related economic activity, according to the local newspaper Post and Courier.
The good news for Charleston, says Dahl, is that local officials are well aware of the problem and have made the city one of the few in the U.S. to publish a comprehensive Sea Level Rise Strategy Plan as far back as 2015, under former mayor Joe Riley. “I do know that Charleston has a good adaptation plan that uses reasonable projections for how much sea level will rise in the coming decades, and that’s not something that every city or state can say,” Dahl says. “There are places that are still just using historic trends rather than looking at the latest science.” Some areas, she says, lack flood maps entirely; others rely only on FEMA maps that are often out of date or fail to incorporate future changes and extreme weather events.
Charleston’s plan outlines a myriad of initiatives focusing on measures like building green infrastructure and improving the drainage system. The city is scrambling to update its drainage infrastructure, some of which dates back to the 1800s, to keep up with recent population growth. Just in the last decade, its population grew by 20 percent, according to the city’s own estimates.
But those preparations are already falling short. In 2017, the Post and Courier reported that after spending over $200 million to tackle a 34-year-old list of necessary drainage and flood mitigation improvements, the city only completed 37 percent of the projects. As a result, normal rainstorms or high tides are enough to flood downtown (and with tainted water).
In 2018 the city announced plans to create its first-ever stormwater department to address the ongoing issues, and the mayor budgeted $2.9 million for this year’s stormwater and flood-mitigation projects. Earlier this summer, the city requested $32 million from the state to raise the 100-plus-year-old Low Battery seawall, at the Charleston peninsula, by 2.5 to 3 feet to accommodate the 1.07-foot rise of the Charleston Harbor since 1921. But the city council and the mayor don’t agree on the project’s priority: Charleston is also seeking $43 million from the state to help fund the construction of a drainage tunnel under a heavily traveled parkway, and if it has to be one or the other, the council voted in August that the mayor must choose the latter project.
For homeowners who live in flood-prone areas and who can afford it, raising their homes is an (expensive) answer to the new climate reality. The city requires homes in flood-prone areas that suffer home damage worth more than half of its value to raise their homes a foot above FEMA’s standards, according to the Post and Courier, which also reported that depending on the location, the minimum level can be as much as 15 feet above sea level.
The city council had earlier this year scrapped a proposed ballot question that would have asked voters whether that one-foot requirement should be raised to two feet—which city leaders say will improve the city’s FEMA insurance rating. Instead, they opted to consider, amongst themselves, whether that new requirement should only apply to new construction and certain vulnerable buildings.
Preservationists were once reluctant to embrace the idea of lifting homes, given Charleston’s historic fabric. But after Tropical Storm Irma flooded dozens of homes downtown in 2017, there was a “huge shift in mindset,” city architect Julia Martin told the Post and Courier. Many homeowners need the lift to prevent insurance premiums from skyrocketing and their home values from plummeting. But it’s an expensive retrofit: One family reported a bill of $475,000 and counting to elevate a historic home, the Post and Courier said—and the city can’t give out federal grants fast enough to meet the increasing demands.
Even without hurricanes, Charleston—and much of coastal South Carolina—faces a future full of grave perils. As projected in a 2018 analysis by the Union of Concerned Scientists, some 16,000 homes in the state, most of them in the Low Country, will flood at least 26 times a year if sea level rise reaches 2 feet by 2045.
At a certain point, chronic inundation would render Charleston uninhabitable. “Parts of the city will likely experience such frequent flooding that it will be difficult to continue living there. They’ll want to relocate,” Dahl says. “Right now, that has been happening at the individual homeowner scale, and it’s happening in the wake of big storms. But there is no comprehensive plan in any one state or at the federal level for how we help people to do that.”
Still, developers continue building in vulnerable areas. A recent study from the nonprofit Climate Central and the real-estate site Zillow found that more than 1,200 homes, valued at $1.27 billion, have been built in South Carolina’s 10-year flood risk zone since 2010. That includes 761 homes in Charleston County. “It is important for Charleston, and really for all coastal locations, to take a hard look at developments underway or slated,” Dahl says, “and ask themselves, ‘Is this wise?’”